the sounding board or chamber. For example, if the strings are laid out parallel to the sounding board and there is no neck, the instrument is a zither whether it is plucked like an autoharp or struck with hammers like a piano. If the instrument has strings parallel to the sounding board or chamber and the strings extend past the board with a neck, then the instrument is a lute, whether the sound chamber is constructed of wood like a guitar or uses a membrane like a banjo. Aerophones, which produce a sound with a vibrating column of air; they are sorted into free aerophones such as a bullroarer or whip, which move freely through the air; reedless aerophones such as flutes and recorders, which cause the air to pass over a sharp edge; reed instruments, which use a vibrating reed (this category may be further divided into two classifications: single-reeded and double-reeded instruments. Examples of the former are clarinets and saxophones, while the latter includes oboes and bassoons); and lip-vibrated aerophones such as trumpets, trombones and tubas, for which the lips themselves function as vibrating reeds. Sachs later added a fifth category, electrophones, such as theremins, which produce sound by electronic means. Within each category are many subgroups. The system has been criticised and revised over the years, but remains widely used by ethnomusicologists and organologists. Schaeffner Andre Schaeffner, a curator at the Musée de l'Homme, disagreed with the Hornbostel–Sachs system and developed his own system in 1932. Schaeffner believed that the pure physics of a musical instrument, rather than its specific construction or playing method, should always determine its classification. (Hornbostel–Sachs, for example, divides aerophones on the basis of sound production, but membranophones on the basis of the shape of the instrument). His system divided instruments into two categories: instruments with solid, vibrating bodies and instruments containing vibrating air. Range Musical instruments are also often classified by their musical range in comparison with other instruments in the same family. This exercise is useful when placing instruments in context of an orchestra or other ensemble. These terms are named after singing voice classifications: Soprano instruments: flute, violin, soprano saxophone, trumpet, clarinet, oboe, piccolo Alto instruments: alto saxophone, french horn, alto flute, english horn, alto clarinet, viola, alto horn Tenor instruments: trombone, tenoroon, tenor saxophone, tenor violin, guitar, tenor drum Baritone instruments: bassoon, baritone saxophone, bass clarinet, cello, baritone horn,